I
recently purchased an old ranch truck.It is a 1973 Chevy with an inline 250 cubic-inch
six-cylinder engine with a four-speed manual transmission.It seemed to
run OK when I got it--considering that it had sat for several years.The odometer only shows
48,000 miles, which the fellow
that I bought it from said was accurate, because his Dad bought it new.He also told me that the
head had been “reworked.”After
I put about 500 miles on the truck, it started
missing badly.I
pulled the spark plugs
and number six was fouled out with black, oily-looking stuff.I put in a new set of
plugs and it ran OK for
about another 400 miles.Number
six had fouled
out again, so I cleaned all of the plugs even though the other five had
only a light-tan
color.I also put
anti-fouling
adapters on all six plugs and reinstalled them.Now, as I try to pull up a hill, the engine wants to
buck and snort.Out
on a level highway, it runs fine and it
idles OK too.What
the heck is going on?

Don’t Run Right

Dear
Don’t Run;

I
am not sure that I can give you a clear-cut answer to this, but I can
give
you a number of suggestions to chase down,isolate
and fix the problem.

First, check
for vacuum leaks.This
applies not only to vacuum hoses, but carburetor and manifold
gaskets as
well.A vacuum leak
allows more air into
the engine without adding the needed fuel, causing a lean air to fuel
mixture.A lean
mixture could cause the engine to misfire, resulting in "bucking and
snorting."Usually,
a vacuum
leak causes poor idling in addition to "bucking and snorting;"
but, you say that the
engine idles OK. However, I have seen stranger things happen with a
vacuum leak.

No
vacuum leak?Next,
I suggest that
you remove the anti-fouling adapters to see if they are causing the
poor hill-climbing problem.If
they are, then
replace them only on the plugs that are fouling out.At least, replace them until you
find
out what is causing spark-plug fouling and correct that
problem.Due to the
age of the truck, I suspect
that the valve-guide oil-seals are shot or they may have been
incorrectly
installed (or left out) when the head was “reworked”.

Still
won’t pull a hill?Now
it is time to
check the ignition timing with a timing light.First, check the base timing, with the
engine idling and the
vacuum-advance hose disconnected and plugged at the distributor.It should be somewhere
between six to ten
degrees BTDC (Before Top Dead Center) for your engine.If that checks out OK, then rev up the
engine while watching the timing-mark on the crankshaft pulley.The RPM's should cause the
centrifugal or
mechanical advance to advance the mark on the pulley.If it doesn’t, then you need to check and free
up the advance-weights and springs in the distributor.If that checks out OK, then it is time to
check the vacuum-advance.With
the
engine still at idle, watch the crankshaft pull mark as you unplug and
put the
vacuum hose back on the vacuum advance.The timing mark should advance.If it doesn’t, then check the advance-chamber for a
vacuum leak
and the hose for blockage and make sure that the hose is connected to
the correct vacuum
connection on the carburetor.

If
all of the above check out OK and the truck still don’t pull
satisfactorilly, it is time for a
compression test.Pull
all of the spark
plugs out and run a compression test on all of the cylinders.Don’t forget to ground the
coil wire or
disconnect the distributor and hold the throttle open while running the
test.The
compression of all cylinders
should be within ten percent of each other and be around 100 PSI.If they are not, then you
are probably in for
some serious engine work, such as pulling the head and grinding or
replacing
valves or tearing the engine down to do a ring job.

If
everything else checks out, then it is time to disassemble, clean and
overhaul the
carburetor.

Covering
the repairs needed for low-compression or overhauling the carburetor
will
require a textbook, not a newspaper article.Good luck.